The present invention relates to a boosting-clamping circuit initially providing a boosted voltage level according to a given input data signal and providing a voltage level lowered and fixed to a predetermined level as time elapses, and to an output buffer circuit having such a boosting-clamping circuit.
The boosting circuit stores charge in a pumping capacitor when the signal supplied to its input terminal is a binary "0" state, and outputs the boosted potential by summing the potential supplied to the input terminal and the potential due to the charge stored in the pumping capacitor, when the signal supplied to the input terminal goes from a binary "0" to a binary "1" state. The boosting circuit is connected to the input terminal of a semiconductor transistor which is turned on or off according to the signal supplied to the input terminal, thereby improving the switching characteristic. However, since the boosting circuit continuously maintains the boosted potential when the signal supplied to its input terminal is a binary "1", the output level of the semiconductor device having the above boosting circuit becomes excessively higher than the reference output level.
Particularly, an output buffer circuit having a pull-up transistor, a pull-down transistor, and the boosting circuit connected to the input terminal of the pull-up transistor, has a fast switching characteristic during the outputting of data "1," but has a slow switching characteristic and high ground noise when outputting data "0" because the output level of data "1" is too high to be rapidly discharged to the low output level of data "0".